It is the purpose of this study to biochemically map the sites of innervation of catecholaminergic neurons in the rat brain by the use of microdissection technique capable of removing specific brain nuclei and a sensitive isotopic assay for norepinephrine, dopamine and DBH. Placement of lesions in the locus coeruleus, dorsal and ventral noradrenergic nerve pathways reveals the contribution of these systems to the innervation of various regions of the brain.